Define

int square(int b) {
  return b*b
}

As you see above code block has a function which work is to square the given number (b ). Some functions return value and some not, which we will be see in a moment.

Creating Functions:

To create (also called by ‘declare’) your own functions, first choose one of the data type (e.g. int,float,bool,etc…) then specify your function name, followed by parentheses ’()’ and curly bracket and done! .

void myFunction() {
  // do something here ....
}

• void is C’s data type. It define what/which type of value should function return. e.g. here void tell C that, this fuction will not return any thing.

Missmatch in declare data type and return value will cause you some headache.

• myFunction() is name of your own fuction followed by ’()’ .

• Inside (or between curly brackets) write your code that, this fuction will execute.

Calling Function

To call function you only need to write name of function (if that fuction required value then pass them to it in ’()’ ).

1 #include <stdio.h>
2 
3 // declare fuction 
4 void sayHello() {
5   printf("Hello, Buddy!");
6 }
7
8 int main() {
9   sayHello(); // call the fuction
10  return 0;
11 }

// Outputs: Hello, Buddy!

You can call fuction multiple time!

4 void sayHello() {
5   printf("Hello, Buddy!");
6 }
7
8 int main() {
9   sayHello(); // call the fuction
10  sayHello(); // we call this again
11  return 0;
12 }

// Outputs: Hello, Buddy!
//          Hello, Buddy!

Arguments/Parameters

The value you pass to your function (inside parentheses ’()’) are known as Arguments/Parameters . Some function need multiple Arguments and some doesn’t need any, depending on work they have to done.

// this function doesn't need any parameters
// also it not return any data
void greeting() {
  printf("Hello, Stranger!");
}

// this function takes two parameters 
//    number1 : integer value
//    number2 : integer value
// also return an integer valur (sum of two number)
int add(int number1, int number2) {
  return number1 + number2
}

Function declaration

C provide you two type of function declaration

• Write function before ‘main()’ function.

// declare function before 'main()' function
void foo() {
  printf("Hello, World!");
}

int main() {
  foo(); 
  return 0;
}

• Declare function name before ‘main()’ function, and write your function anywhere in program.

// declare function name before 'main()' function
int sum(int a, int b)

// main() function
int main() {
  sum(12,1); // call function
  return 0;
}

// function defination
int sum(int a, int b) {
  return a + b;
}

C Hello World

Sep 2, 2022